OBSERVATIONS ON THE AQUARIA AT CENTRAL STATION. 
3 
watercock, conveniently located, by means of small rubber tubing. The higher it car 
be carried, the greater will be the force created. The fall should be 8 or 10 feet at 
least, and 20 or more feet will make it much more efficient. The higher it is carried, 
however, the stronger the tubing must be. From this tube a small stream of water, 
cut down to a gentle flow, is allowed to drop into another tube having an enlarged 
mouth and of one-fourth to three-eighths inch bore, drawing in with it air, thus inducing 
capillarity, the air forming into globules or bubbles alternating with water spaces, as 
shown in fig. A 1, plate iv. 
In the illustration the tube is shown as being attached directly to the cock and 
with a hole in the side for the induction of air. This method of attachment is probably 
the best, and might be made more effectual by the use of a metal supj)ly-pipe. 
Some provision is necessary for carrying off the water in case of any accidental 
stoppage of the pump, as when the water is prevented from passing down the tube 
it finds its way out of the air-hole at the top. A funnel-shaped receiver with a nipple 
inserted into the side, to which may be attached a piece of small rubber tubing lead- 
ing to a sink or other exit, might be placed on the tube below the air-hole and would 
probably be as simple and effective as anything; but this can be left to individual 
ingenuity. 
A small nozzle has been used through which to pass the water into the tube (A 1) 
with force, but it is probably no more efficient, while great strain is brought on the 
tubing attaching it, often causing it to burst, and it is also liable to become choked by 
small crustaceans, scale from the water-pipes, etc. 
Through the tube (A 1), which is an enlarged sketch of what would be the top of 
the supply tube (A 2), the air and water pass into ajar, B, which has, in addition to 
the entrance or supply tube, two exit tubes, all passing through an air-tight cork or stop- 
per, 0. One of these tubes, D, merely passes through the stopper and is for the exit 
of the air, which of course remains in the upper part of the jar or above the water, while 
the longer one, extending to the bottom of the jar, is for the exit of the water. 
A proper regulation of the height of the overflow-pipe outside the jar will regulate 
the flow of air into the aquarium. This regulation is necessary to equalize the pressure, 
as it will vary with the proportion of air and water passing into the jar, the depth of 
water in the aquarium, etc. 
Several forms of liberators for the air passing into the aquaria have been devised. 
The difficulty in efficient aeration in this way has been in the tendency of the escaping 
globules of air to coalesce and form large bubbles. The more finely the air can be 
comminuted the more rapidly it will be absorbed by the water, and consequently the 
more perfect the aeration will be. Many kinds of dead wood, which are porous, such 
as grape-vine, have been found to liberate the air in very minute bubbles, and sponge 
properly inserted into the mouth of a glass tube bent in the shape of a hook so that the 
mouth will open upwards has worked well. It is probable that many other more 
satisfactory porous materials may be found. 
The original supply of salt water was brought from Chesapeake Bay, and from 
time to time when the Commission’s steamer, the Fish Hatch, returns to Washington 
an additional supply is obtained. This, however, does not supply all loss from various 
causes and artificial sea water has sometimes been used. This has been made by using 
a salt produced by evaporating sea water. 
